In recent years, as a result of the development of semiconductor process, integrated circuits often drive relatively large current loads, such as an LED (light emitting diode).
There are various devices for driving an LED by using a battery as a power supply. Japanese Laid-Open Patent Publication No. 8-23,578 (Andou et al.) shows a remote controller for driving an LED having a controller with a capacitor, and a battery. FIG. 8 shows a circuit diagram of Andou et al.'s remote controller. The capacitor 8 is connected to the Vdd and the ground ofthe controller 3 in order to supply power to the controller 3. A diode 2 is provided between an anode of the battery 1 and a positive electrode of the capacitor 8. The diode 2 connects the battery 1 to the controller 3 when a battery voltage Vb' is larger than a capacitor voltage Vc' by 0.6 V, which is forward voltage of the diode 2. Otherwise, the diode 2 disconnects the battery 1 from the controller 3. Based on an operating switch 7, the controller 3 switches a transistor 4 which drives an LED 6. A resistor 5 limits current flowing through the transistor 4 and the LED 6.
Andou et al.'s remote controller suffers from inherent limitations. For example, due to the forward voltage of the diode 2, the capacitor voltage Vc' cannot be larger than (Vb'-0.6 V). Moreover, Andou et al.'s controller does not provide connection and disconnection between the battery 1 and the capacitor 8 based on the switching state of the controller 3. These disadvantages eliminate Andou et al.'s device as a viable alternative since the battery voltage Vb' is usually low, and thus the further lower voltage of (Vb'-0.6 V) is not desirable for efficiently supplying the controller 3. Andou et al. does not provide the connection based on the switching state of the controller 3, which is preferable in some cases.